Motorboat activity can adversely effect the water quality of a reservoir. The potential impacts of motorboat activity on the Occoquan Reservoir's water and sediments were evaluated. Thirty-one sites, both marina and nonmarina, along the reservoir were selected. Sediment and water samples were collected in 1990, during peak boating activity, and in October, during low boating activity. The objectives of this research were to determine the concentrations of polyaromatic hydrocarbons (PAHs) in water and sediment samples and to determine if their presence was related to boating activity. The presence of other non-PAH organics was also determined. Contours of total PAH concentrations, boxplots and ANOVA analyses between marina and nonmarina sites were generated from gathered data in order to meet these objectives. PAHs were present in the water during peak boating activity and not detected during low boating activity, while PAHS were detected in the sediments during both sampling periods. The aqueous and sediment PAH concentrations were at or below the method detection limits. The PAH ratios of unalkylated PAHs confirmed PAH contamination to be of a combustion source. Boating was shown to be a PAH source to the water column, during peak boating activity, throughout the entire Occoquan Reservoir. An ANOVA between marina and nonmarina sites for the aqueous total PAH concentrations did not show a significant difference in June. This implied that boating did not cause any localized impacts to the water column and that there was another PAH source. There was a significant difference for total PAH concentrations between the marina and nonmarina sites for the sediment samples in June, showing localized impacts at marina areas due to boating activity. PAH profiles showed urban runoff as another major contributor to the PAH concentration in the water and sediments. The urbanization of Hooes Run and the hydrology of the reservoir caused urban runoff to impact localized areas. Finally, atmospheric deposition was also a source of PAHs to the sediments throughout the entire reservoir. Non-PAH organics found in a few of the water and sediment samples were the pesticides atrazine and p,p'-DDD, alkyl phosphates, alcohols and C₈ to C₁₂ hydrocarbons. / Master of Science

This project reviewed the ability of hydrilla to release THM-precursors should this plant become established in the Occoquan Reservoir. It was found that the Occoquan Reservoir could support hydrilla. Three sources of THM-precursors were found to result from hydrilla. These included: 1) extracellular products (ECP) from hydrilla itself; 2) ECP from periphyton that colonized the hydrilla; and 3) decay products from hydrilla. This study projected aa potential increase in THMFP of 23 ug/L should hydrilla become established in the Occoquan. The current level of THMFP in the H reservoir is approximately l,OOO ug/L. / Master of Science

The phytoplankton data from Occoquan Reservoir surface samples collected during 1970-1988 were entered into a database. The data were analyzed to determine the relationships between changes in phytoplankton succession patterns and the various physical and chemical water-quality variables. The investigation considered the variations in both the phytoplankton and the water-quality variables with respect to sampling station location along the length of the reservoir. The variables included rainfall, season, pH, alkalinity, nitrogen, phosphorus, copper sulfate, odor intensity and type, and chlorophyll-a. The discharge from the Upper Occoquan Sewage Authority advanced wastewater treatment plant (UOSA AWT) had a noticeable influence on both the phytoplankton division dominance and the genera occurrence. Before the AWT plant was built, Chlorophycota was usually dominant; afterwards, Bacillariophycota dominance increased. The dominant genera were a subset of the genera that occurred frequently. Of the original 72 genera, an analysis of 9 prevalent genera would have provided virtually the same information. Neither the intensity nor type of odors observed were predictable on the basis of the phytoplankton genera present in the reservoir. No statistically valid conclusion could be reached about the impact that copper sulfate applications had on reservoir algae. / Master of Science

Increased salinity in freshwater systems – also called the Freshwater Salinization Syndrome (FSS) – can have far-ranging implications for the natural and built environment, agriculture, and public health at large. Such risks are clearly on display in the Occoquan Reservoir – a drinking water source for roughly one million people in the northern Virginia/ National Capital Region. Sodium concentrations in the Occoquan Reservoir are approaching levels that can affect taste and health. The Reservoir is also noteworthy as a flagship example of indirect potable reuse, which further adds complexity to understanding the sources of rising levels of sodium and other types of salinity. To help understand the role residential discharges might play in salinization of the Occoquan Reservoir, a suite of laundry detergent products was identified based upon survey data collected in the northern Virginia region. The ionic compositions of these products were then characterized using ion chromatography and inductively coupled plasma-mass spectrometry to quantify select ionic and elemental analytes. Sodium, chloride, and sulfate were consistently found in appreciable amounts. To comparatively characterize the laundry detergents, principal component analysis was employed to identify clusters of similar products. The physical formulation of the products was identified as a marker for their content, with dry formulations (free-flowing and encapsulated powders) being more enriched in sodium and sulfate. This result was corroborated by comparing nonparametric bootstrap intervals for individual analytes. The study's findings suggest an opportunity wherein consumer choice can play a role in mediating residential salt inputs in receiving bodies such as the Occoquan Reservoir. / Master of Science / Many streams, rivers, and other freshwater systems have become increasingly salty in recent decades. A rise in salinity can be problematic, stressing aquatic life, corroding pipes, and even enhancing the release of more pollutants into the water. This phenomenon, called Freshwater Salinization Syndrome, can threaten such systems' ability to serve as sources of drinking water, as is the case for the Occoquan Reservoir in northern Virginia. Serving roughly one million people, the Reservoir is notable for being one of the first in the country to purposely incorporate highly treated wastewater upstream of a drinking water supply. Despite the Reservoir's prominence, the reasons behind its rising salt levels are not well understood. This study sought to understand the role that individual residences could play when household products travel down the drain and are ultimately discharged into the watershed. Laundry detergents are potentially high-salt products. A survey of northern Virginian's laundry habits was conducted to understand local tastes and preferences. Informed by the survey, a suite of laundry detergents was chemically characterized to measure salt and element concentrations. The detergents were found to have notable amounts of sodium, chloride, and sulfate in particular, with sodium being the most abundant analyte in every detergent. However, not all detergents were equally salty; statistical tools revealed that dry formulations (such as powdered and powder-filled pak detergents) contributed more sodium and sulfate, among other things. This study's findings suggest that laundry detergents could be contributing to Freshwater Salinization Syndrome in the Occoquan Reservoir, and that local consumers' choice of detergents could make a difference.